1. Field of the Invention
The present invention relates to automatic focusing photographic cameras in general, and to control systems for positioning the adjustable focus lens in such cameras, in particular.
2. Description of the Prior Art
Photographic cameras having interchangeable fixed and/or adjustable focus lenses are well known in the prior art. Cameras having an adjustable focus lens and having a focus control system coupled to said lens for automatically focusing image forming light rays from a remote object at the film plane of such a camera in response to a rangefinder derived signal representative of the actual distance between said camera and said remote object, are also known in the prior art. A camera having such a focus control system and utilizing acoustical energy to determine the distance to a remote object is described in U.S. Pat. No. 3,522,764 to BIBER et al.
In an adjustable focus lens, there is a well understood nonlinear relationship between the axial position of the movable element in such a lens where a subject to be photographed is in focus at a particular image plane, and the distance from such a subject to said adjustable focus lens. When designing an automatic focus control system for an adjustable focus lens camera such as that described in the above-mentioned BIBER et al. patent, consideration must be given to this nonlinear relationship. If the adjustable focus lens of such a camera is replaced with another adjustable focus lens without due regard for the lens position/subject distance relationship of said replacing lens, misfocusing of said replacing lens will result if there is a significant difference between the lens/subject function of the replaced lens and the lens/subject function of the replacing lens.
In order to be able to interchange one adjustable focus lens in an automatic focusing camera of the type described above, with a different adjustable focus lens having a significantly different lens/subject function as discussed above, the control system of said camera must be readily modifiable such that it is capable of positioning said different adjustable focus lens with its significantly different lens/subject function to the correct subject-in-focus position. If a fixed focus lens is to be combined with an existing adjustable focus lens in an automatic focusing camera as when a fixed focus telephoto lens is optically coupled to an adjustable focus lens, means must be provided for readily scaling up or scaling down the magnitude of the lens/subject function of said adjustable focus lens to compensate for the magnification provided by said fixed focus lens.